The present invention relates to a process for the stripping of cesium ions from aqueous solutions in which a precipitation agent is added to the aqueous solution and the resulting precipitate, containing the Cs.sup.+ ions, is stripped from the solution.
Cs-137 in its property as hard gamma ray emittor, is a particularly undesirable fission product in medium radioactive aqueous waste products (MAW), and renders more difficult the processing and solidification of MAW. A prior selective stripping of the Cs-137 would considerably simplify the further processing of medium radioactive waste products. After stripping the Cs-137 from the MAW, the shielding of the concentrate and/or the solidified ultimate waste package could be totally or at least partially omitted. In addition, such a process could also be profitably used for obtaining or stripping of Cs isotopes from highly active waste solutions as they occur, for example, in the reprocessing of nuclear fuels in the first extraction cycle. Here, the extraction of pure isotopes or isotope mixtures of cesium would be of practical importance for radio-chemical use and as radiation or heat source.
In the past, attempts have been made to precipitate Cs.sup.+ ions with sodium tetraphenylborate (commercial name Kalignost), but it has been determined that such a precipitation cannot be done either selectively or in an acid milieu.
The stripping of cesium is done, according to a known process, mainly by coprecipitation reactions. However, the coprecipitation does not supply satisfactory decontamination factors for Cs (DF values). Thus, other processes were locked for which would permit a selective stripping of the cesium radionuclides.
The extraction procedures which have so far been developed for Cs.sup.+ ions are not suitable for stripping Cs.sup.+ from a typical MAW with its high content of NaNO.sub.3 and free nitric acid.
J. Rais and P. Selucky proposed an extraction system for stripping Cs.sup.+ from aqueous solutions, which uses 2,3,11,12-dibenzo-1,4,7,10,13,16-hexa-oxo-cyclo-octadeca-2,11-dien (dibenzo-18-crown-6DB-18-C-6 for short) in an organic phase and sodium tetraphenylborate was added to the aqueous phase which forms a Cs.sup.+ containing adduct to be extracted. (Czechoslovakian Patent CS-PS No. 149,404). However, the process is limited to alkaline Cs.sup.+ solutions (pH 11 to 13) because sodium tetraphenylborate is hydrolyzed in the acid range. In addition, the process only works well in the absence of substantial amounts of Na.sup.+ and K.sup.+.